Motorized seat belt retractor

ABSTRACT

A motorized seat belt retractor having a load limiter to control the tensile load on a seat belt webbing, especially when the webbing is withdrawn due to an emergency condition. The load limiter controls the tension by controlling the condition of the motor that drives the retractor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 09/838,281 filed on Apr. 20, 2001 now U.S. Pat. No.6,676,060 claiming priority to and the benefit of U.S. ProvisionalPatent Application Serial No. 60/198,751 filed Apr. 21, 2000. Theforegoing applications are each incorporated by reference herein intheir entireties.

BACKGROUND OF THE INVENTION

The present invention relates to a seat belt retractor with a loadlimiter and a locking mechanism. More particularly, the presentinvention relates to a retractor having a motorized load limiter andlocking mechanism.

Conventionally, retractors have include a mechanical load limiter suchas a torsion bar or the like for limiting the load applied on a shoulderor chest of an occupant of a motor vehicle. In these conventionalretractors the mechanical type of load limiter does not allow for thethreshold setting for load on the webbing to be altered. Typically, thethreshold value for the amount of tensile load to be applied to thewebbing is determined according to the model type of automobile. Thisthreshold value is fixed and cannot be easily altered.

Therefore, it is desired to develop a novel retractor in which thethreshold value for tensile load on the seat belt webbing is adjustable.

SUMMARY OF THE INVENTION

To achieve the aforementioned object, the present invention provides amotorized seat belt retractor having a load limiter for controlling thetensile load on a webbing withdrawn in the event of emergency. The loadlimiter utilizes force generated by rotation of the motor shaft tocontrol the tensile load. This approach to a load limiter is novel andmay include a high-voltage motor having improved motor current risingcharacteristics during starting of the motor.

According to the structure of the present invention, the force generatedby the rotation of the shaft of the motor can be utilized as the tensileload for the load limiter. This configuration allows for the easyadjustment of the threshold value of the tensile load on the webbing andpermits the threshold value to be set over a wider range of possiblevalues.

The load limiter of the motorized seat belt retractor includes arotational resistance generating means which generates a rotationalresistance force in response to the rotation of the shaft of the motor.According to this structure, during rotation of the shaft of the motor arotational resistance force is generated due to the inertial moment ofthe shaft, this rotational resistance force can be positively utilizedto control the tensile load on the webbing.

In the aforementioned motorized seat belt retractor which includes aload limiter for controlling the tensile load on a webbing withdrawn dueto forward movement of an occupant in the event of emergency, the loadlimiter includes a rotational resistance generating means which providesfor the generation of a rotational resistance force by the motor whenthe motor is short circuited. According to this structure, therotational resistance force generated by the motor when short circuitedcan be positively utilized as the tensile load for the load limiter,thereby eliminating the necessity of a separate mechanical load limiter.Thus, the present invention provides for manufacturing motorized seatbelt retractors of a smaller size and at a low cost.

According to the present invention, the rotational resistance generatingmeans of the motorized seat belt retractor generates a rotationalresistance force by switching the motor into either the short circuitedstate or the non-short circuited state according to predeterminedsequence control. According to this structure, a desired tensile load onthe webbing can be obtained by suitably setting the period in which themotor is in the short circuited state and the period in which the motoris in the non-short circuited state and sequentially switching the shortcircuited state and the non-short circuited state of the motor.

In the motorized seat belt retractor, the non-short circuited state canmean that the motor is energized. According to this structure, thetensile load on the webbing can be controlled by utilizing therotational torque of the motor. The rotational resistance force of themotor in the non-short circuited state (i.e., energized state) isadjustable, thereby allowing a wider range for the setting value of thetensile load on the webbing.

In the motorized seat belt retractor, the non-short circuited state canmean that the motor is electrically connected via a resistor. Accordingto this structure, the rotational resistance force of the motor in thenon-short circuited state can be adjusted by changing the resistancevalue of the resistor, thereby allowing a wider range for the settingvalue of the tensile load on the webbing.

In the motorized seat belt retractor, the non-short circuited state canmean that the motor is electrically open. According to this structure,little rotational resistance force is generated by the motor in thenon-short circuited state when the motor is electrically disconnected(open-circuit), thereby easily allowing a wider range for the settingvalue of the tensile load on the webbing at a low cost without anycomplex mechanism.

The load limiter of the motorized seat belt retractor includes a geartrain which couples the shaft of the motor to a spool on which thewebbing is wound. According to this structure, the tensile load on thewebbing can be controlled not only by adjusting the rotationalresistance force of the motor but also by changing the gear ratio of thegear train.

In the aforementioned rotational resistance generating means whichgenerates rotational resistance force by the motor, the rotationalresistance force further acts for preventing a rotational shaft of amotor from rotating in a direction of withdrawing the webbing. Accordingto this structure, the rotating shaft of the motor is electricallylocked, thus preventing rotation of the shaft at a suitable timing.

According to the present invention, described in general above, it ispreferred that the rotational resistance force be generated at least bycounter-electromotive force generated by the rotation of the rotationalshaft of the motor when short circuited. According to this structure,the counter-electromotive force generated by the rotation of therotational shaft of the motor when short circuited can be utilized asthe locking mechanism, thereby eliminating specific control for drivingthe motor.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become apparent from the following description, appendedclaims, and the accompanying exemplary embodiments shown in thedrawings, which are briefly described below.

FIG. 1 is an exploded perspective view showing an embodiment of aretractor according to the present invention.

FIG. 2 is an explanatory view showing the mesh relation between gears ofthe retractor of the embodiment according to the present invention.

FIG. 3 a is a view illustrating a state where the motor is rotated inthe clockwise direction (CW direction) and

FIG. 3 b is a view illustrating a state where the motor is rotated inthe counterclockwise direction (CCW direction).

FIG. 4 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point in this figure) to a point where the vehiclecompletely crashes. Curves indicate cases which are different in theweight (Light, Middle, Heavy) of occupant in the vehicle, respectively.

FIG. 5 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point in this figure) to a point where the vehiclecompletely crashes. Curves indicate cases which are different in thecollision speed (Low, Middle, High) of the vehicle, respectively.

FIG. 6 a is a circuit diagram of the circuit including the retractor dcmotor and a variable resistor.

FIG. 6 b is a circuit diagram of the circuit including the retractor dcmotor and a fuse.

FIG. 7 is a graph of the dc current/voltage applied to the retractormotor versus time.

DETAILED DESCRIPTION

Hereinafter, an embodiment of the present invention will now bedescribed with reference to the drawings. It should be understood thatthe sizes, shapes, positional relation of respective components areschematically shown just for understanding the invention and that thenumerical conditions stated in the following are just illustrativeexamples.

Hereinafter, an embodiment of a retractor according to the presentinvention will be described. FIG. 1 is an exploded perspective viewshowing the embodiment of the retractor according to the presentinvention. FIG. 2 is an explanatory view showing the mesh relationbetween gears of the retractor of this embodiment. It should be notedthat the illustration of a pyrotechnic pretension mechanism is omittedin FIG. 1.

The structure of the retractor of this embodiment will now be describedwith reference to FIGS. 1, 2. The retractor 200 comprises the followingcomponents: a retainer 20; a DC motor 21 attached integrally to theretainer 20; a pinion 22 attached integrally to a motor shaft of the DCmotor 21; a first gear 23 which is journalled by a projection formed onthe retainer 20 and is in mesh or engaged with the pinion 22. The firstgear 23 is preferably an integral double gear comprising a large gear 23a and a small gear 23 b. The pinion 22 is positioned to mesh with thelarge gear 23 a.

The retractor also includes a second gear 24 which is journalled by aprojection formed on the retainer 20 and is in mesh or engaged with thefirst gear 23. In particular, the retainer is engaged with the smallgear 23 b. The second gear 24 is preferably an integral double gearcomprising a large gear 24 a and a small gear 24 b. The small gear 23 bis in mesh or engaged with the large gear 24 a.

The retractor further includes a third gear 25 which is in mesh with thesecond gear 24. In particular, the third gear is engaged with the smallgear 24 b. The third gear 25 is preferably an integral double gearcomprising a large gear 25 a and a small gear 25 b. The small gear 24 bis in mesh with the large gear 25 a.

The retractor also includes three planetary gears 26 which are in meshwith the third gear 25. The planetary gears engage the small gear 25 b.An internal gear 27 is also provided. The internal gear 27 has internalteeth 27 a which engage with the three planetary gears 26. The internalgear 27 includes external ratchet teeth 27 b formed in the outerperiphery of the internal gear 27.

A pawl 30 is provided to engage with the external ratchet teeth 27 b,and to thereby stop the rotation of the internal gear 27 in theclockwise direction. The pawl 30 is supported at a lever 31 comprising aspring at an end connected to the pawl 30. The other end of the lever 31includes a portion curled to form a ring member 32 that is formed in acurled portion of the other end of the lever 31. The ring member 32 iswound on a projecting disk-like member 33. The disk-like member 33 isintegrally formed coaxially with the first gear 23. A frictional piece34 projects from the outer periphery of the disk-like member 33 andpresses against the ring member 32 to apply friction.

The three planetary gears 26 are positioned on a carrier 35. Three pins36 are provided for rotatably supporting and securing the threeplanetary gears 26 to the carrier 35. A speed-reduction plate 37 isinterposed between the three pins 36 and the three planetary gears 26.

A webbing W for restraining an occupant's body of which one end is fixedto a spool 38. As shown in FIGS. 2 and 3 arrow A designates a directionof withdrawing the webbing W and arrow B designates a direction ofretracting the webbing W. The spool 38 includes a tip portion 38 a thatpasses through a rotational central hole of the carrier 35. The tipportion 38 a also passes through the rotational central hole of thethird gear so as to be both slidable and rotatable relative to the thirdgear. On the other hand, the root of the tip portion 38 a is fitted andfixed to the carrier 35.

The retractor includes a cover 39 covering the entire of the forcetransfer mechanism or gear train. A plurality of screws 40 are providedfor fixing the cover 39 to the retainer 20.

A control circuit controls the connection of the DC motor 21 to beshort-circuited or non-short-ciruited and also controls the rotation ofthe DC motor 21 in the clockwise (CW) direction or in thecounterclockwise (CCW) direction.

As described herein, when the motor 21 is short circuited, no drivingcurrent is supplied to turn the motor shaft. In this condition, when theshaft of the motor attempts to rotate due to the rotational forcetransferred from the first gear and engaged pinion a counterelectromotive force resists movement of the motor shaft.

As described herein, when the motor is non-short-circuited the motor maybe located in an open-circuit or may be connected to a DC power sourcewhich supplies a driving current that generates a rotational force todrive the shaft in a chosen direction.

Hereinafter, description will now be made as regard to the operation ofthe retractor of the present invention with the aforementionedcomponents.

FIGS. 3(A) and 3(B) illustrating the operation of this embodimentwherein FIG. 3(A) is a view illustrating a state where the motor isrotated in the clockwise direction (CW direction) and FIG. 3(B) is aview illustrating a state where the motor is rotated in thecounterclockwise direction (CCW direction).

In the retractor 200, as shown in FIG. 2 and FIG. 3(B), the engagingpawl 30 is spaced apart from the external ratchet teeth 27 b so that theinternal gear 27 is not restricted in the normal state (i.e., not in anemergency such as emergency braking or a vehicle collision). In thisnormal state, because of the property of the planetary gear train, therotational torque of the carrier 35 is not transmitted to the thirdgear. Therefore, the rotational torque of the spool 38 integrally fittedand fixed to the carrier 35 is not transmitted to the rotational shaftof the DC motor 21, which is indirectly engaged with the third gear.

In the event of emergency, such as emergency braking and a vehiclecollision, a pretensioning mechanism (for winding up the webbing W toincrease the tension prior to the pyrotechnic pretension mechanism) isactuated according to output signals from an ABS (anti-skid or brake)mechanism (not shown) and/or a collision predictive device (not shown)in order to rotate the rotational shaft of the DC motor 21 in the CWdirection as shown by the arrow in FIG. 3(A). Then, the rotationaltorque of the pinion 22 in the clockwise direction is transmitted to thefirst gear 23 as a rotational torque in the counterclockwise direction(indicated by arrow). As a result, the pawl 30 engages with one of theexternal ratchet teeth 27 b of the internal gear 27 to stop the rotationof the internal gear 27 in the clockwise direction (indicated by arrow).Therefore, the rotational torque of the third gear 25 can be transmittedto the carrier 35, which is integrally fitted and fixed to the spool 38.

In the case of the emergency condition, the rotational torque of thefirst gear 23 is transmitted to the second gear 24 as rotational torquein the clockwise direction (indicated by arrow). In addition, the torqueis further transmitted to the third gear 25 as rotational torque in thecounterclockwise direction (indicated by arrow). Due to the rotation ofthe third gear 25 in the counterclockwise direction, the small gear 25 bof the third gear 25 is rotated in the counterclockwise direction so asto apply rotational torque in the clockwise direction (indicated byarrow) to the three planetary gears 26. The three planetary gears 26rotate in the counterclockwise direction (indicated by arrow) likeplanets around the small gear 25 b and, during this rotation, engagewith the internal teeth of the internal gear 27. The internal gear 27 isstopped from rotating by the pawl 30. Therefore, the carrier 35 rotatesto journal the three planetary gears 26 in the counterclockwisedirection (indicated by arrow). Because the spool 38 is fitted and fixedto the carrier 35, which is rotating in the counterclockwise direction,the spool also rotates in the counter clockwise direction to wind up thewebbing W (in the direction of arrow B).

Thereby, as described above, the rotational torque generated by theshaft of the DC motor 21 rotating in the clockwise direction istransmitted to the spool 38 as rotational torque for winding up thewebbing W.

As impact is exerted on a vehicle body due to a vehicle collision,impact detecting signals are outputted from an acceleration sensor (notshown) and/or a crush sensor (not shown) whereby a pyrotechnicpretension mechanism (not shown) is actuated to retract the webbing Winto the retractor 200, as described above, thereby ensuring initialrestraint of the occupant.

After the collision or impact occurs, the webbing W will be withdrawn(in a direction of arrow A in FIG. 3(A)) by the inertial force of theoccupant moving forwardly due to the collision. During this movement ofthe webbing W and the spool 38, as shown in FIG. 3(A), the torqueapplied to the spool 38 by withdrawing of the webbing W is transmittedto the DC motor 21 as rotational torque in the counterclockwisedirection (in a direction opposite to the direction of arrow) becausethe engaging pawl 30 is engaged with the external ratchet teeth 27 b.When the DC motor is short-circuited (i.e., the terminals are connected,but no external voltage is applied), the movement of the DC motor shaftcreated by the occupant's motion is opposed by a counter electromotiveforce (“counter emf”). As a result, the motor shaft provides arotational resistance force that acts to prevent the rotation of thespool 38 and withdrawal of the webbing W.

The present invention provides for using the rotational resistance forcecreated by the rotating DC motor shaft to provide a locking mechanismand/or the EA mechanism. It should be noted that the term “EA” is anabbreviation of “energy absorbing” meaning that impact (load) acting onan occupant's body is absorbed by a seat belt, and this term will beused generally hereinafter.

The characteristics of the rotational resistance force will now bedescribed with reference to the drawings. FIG. 4 is a graphschematically showing the relation between the rotational resistanceforce F [Nm] (Newton meter) provided by the short-circuited DC motor andtime T [sec] (second) from a point where a vehicle collides with a wall(0 point of this graph) to a point where the vehicle completely crashes.The three curves shown in FIG. 4, indicate situations where differentweight occupants were located in the vehicle (i.e., Light, Middle andHeavy occupants).

FIG. 5 is a graph schematically showing the relation between therotational resistance force F [Nm] (Newton meter) of the short-circuitedDC motor and time T [sec] (second) from a point where a vehicle collideswith a wall (0 point of this graph) to a point where the vehiclecompletely crashes or comes to rest. Curves indicate cases which aredifferent in the collision speed (Low, Middle, High) of the vehicle,respectively.

As shown in FIG. 4, in the case of a light-weight occupant, the risingslope or inclination of the curve is relatively gentle (the solid linein the graph of FIG. 4). In the case of a heavy-weight occupant, therising inclination of the curve is steep (the two-dot chain line shownin FIG. 4). In the case of a medium-weight occupant, the risinginclination of the curve is middle between the case of the light-weightoccupant and the case of the heavy-weight occupant. Regardless of theoccupant's weight, the descending slope or inclination of all of thecases are gentle.

Accordingly, by using the rotational resistance force as the EAmechanism, EA load is relatively gently increased against thelight-weight occupant so that the total load on the light-weightoccupant is relatively small. On the other hand, EA load is relativelysteeply increased against the heavy-weight occupant so that the totalload on the heavy-weight occupant is relatively large. The decrease inEA load is gentle regardless of the occupant's weight, achieving “softlanding” (it means “decrease in belt tension acting on the occupant isgentle with time elapsing”).

As shown in FIG. 5, the higher the speed of the vehicle when collidingwith a wall, the higher the load limit of the rotational resistanceforce F (EA load limit) (the two-dot chain line in the graph of FIG. 5).The lower the speed of the vehicle when colliding with a wall, the lowerthe load limit of the rotational resistance force F (the solid line inthe graph of FIG. 5). That is, the load limit is increased or decreaseddepending on the collision speed, exhibiting the ideal occupantrestraint performance.

In case of conventional mechanical EA mechanism (e.g. a torsion bar) therising inclination of EA load is constant so that the load limit is alsoconstant regardless of the occupant's weight and the collision speed.The present invention improves on conventional methods and devices.

The load limit can be freely set in various manners as follows. Forexample, The gear ratio of the gears located between the shaft of the DCmotor 21 and the web spool 38 may be changed. A change in gear ratiochanges the load limit of the rotational resistance force transmittedfrom the motor 21 to the spool 38. Also, a change in gear ratio changesthe rising and descending slope of the force over time shown in FIG. 4.

Further by way of example, the DC motor 21 may be attached to a circuitthat includes a variable resistor 40, as shown in FIG. 6 a. The value ofthe resistor 40 may be changed in order to change the load limit of theforce being transferred from the motor to the web spool 38. Similarly,the value of resistance may be changed to adjust the rising inclinationand the descending inclination of the curves shown in FIG. 4. As thevalue of resistance is increased, the amount of force transferred fromthe motor 21 to the web spool 38 decreases. As a result, the load limitdecreases, the rising inclination becomes gentler, and the descendinginclination becomes steeper. In this case, a plurality of resistorshaving different values of resistance may be positioned in parallel andselectably connected to the circuit in such a manner as to automaticallyconnect to a resistor having a value best suited to achieve idealrestraint performance.

Still further by way of example, a fuse 42 may be connected to the powersupply for the motor 21, as shown in FIG. 6 b. The EA mechanism providedby the motor 21 can be released by opening the fuse and open-circuitingthe motor to lower the EA load when current exceeds a predeterminedvalue.

As described above, the DC motor 21 may be energized by a drivingcurrent to rotate in a direction for retracting the webbing W (thedirection of arrow in FIG. 3(A)). Rotation in this direction provides arotational resistance force opposite to the force provided by theoccupant. On the contrary, the rotational shaft of the DC motor 21 maybe rotated in the direction of withdrawing the webbing W (the directionopposite to the direction of arrow in FIG. 3(A)), to provide a forcethat subtracts from the conventional rotational resistance force.

The load limiter can also function as a locking mechanism, by providingsufficient rotational resistance force to cancel the rotational torqueof the spool 38 acting in a direction of withdrawing the seat belt.

Alternatively, the motor 21 may be replaced with another one havingdifferent output. Thus, the load limit of the rotational resistanceforce F, the rising inclination, and the descending inclination can beadjusted by changing the motor rating.

As shown in FIG. 7, the time period t1 of short circuit of the DC motor21 and the time period t2 of non-short circuit of the DC motor 21 may befreely changed to make a pulse-like rectangular wave in order to adjustthe load limit of the rotational resistance force F, the risinginclination, and the descending inclination of the resistance force. Forinstance, as the time period t1 is set longer than the time period t2,the load limit becomes higher, the rising inclination becomes steeper,and the descending inclination becomes gentler. On the contrary, as thetime period t2 is set longer than the time period t1, the load limitbecomes lower, the rising inclination becomes gentler, and thedescending inclination becomes steeper.

The timing for starting the EA mechanism can be controlled by an ECU(“Electronic Control Unit”) for commanding the ignition timing of anairbag device or an ECU for a pretension mechanism.

It is preferable that the load limit of the rotational resistance forceF, the rising inclination, and the descending inclination are suitablyset according to the withdrawal characteristic of webbing W which isobtained from experiments using real cars with dummies.

A rotational shaft with a magnet in a copper tube may be used instead ofthe DC motor 21, thereby removing the requirement to energize the motorand, thus, making EA mechanism at a low cost and with a simplestructure.

Combinations of the EA mechanism and various pretension mechanisms suchas a back pretensioner may provide more advantages. Further, a vehiclesensor may be incorporated in the retractor as an EA switch.

The method of using the rotational resistance force of theshort-circuited motor as EA mechanism according to the present inventioncan be applied to a retractor of another type just like theaforementioned embodiment shown in FIG. 1.

As discussed above, the present invention achieves suitable timing oflocking.

Given the disclosure of the present invention, one versed in the artwould appreciate that there may be other embodiments and modificationswithin the scope and spirit of the invention. Accordingly, allmodifications attainable by one versed in the art from the presentdisclosure within the scope and spirit of the present invention are tobe included as further embodiments of the present invention. The scopeof the present invention is to be defined as set forth in the followingclaims.

1. A motorized seat belt retractor comprising: a motor having a motorshaft; a load limiter for controlling the tensile load on a webbingwithdrawn in the event of emergency; wherein the load limiter isconfigured to utilize a force generated by the rotation of the motorshaft to thereby control the tensile load on the webbing, wherein theload limit is controlled using a fuse located in series with the motorin an electrical circuit configured to carry a driving current to themotor, wherein the load limiter is configured to control the tensileload on the webbing by alternatively placing the motor in ashort-circuit and non-short-circuit condition according to apredetermined sequence.
 2. The motorized seat belt retractor of claim 1,wherein the fuse is configured to open at a predetermined value ofcurrent flow through the circuit to thereby open-circuit the motor andcontrol the load limiter.
 3. The motorized seat belt retractor of claim1, further comprising an electrical controller configured to establishthe predetermined sequence.
 4. The motorized seat belt retractor ofclaim 3, wherein the fuse is configured to open at a predetermined valueof current flow through the circuit to thereby open-circuit the motorand control the load limiter.
 5. The motorized seat belt retractor ofclaim 1, wherein said load limiter includes a mechanism for transferringthe farce generated by the rotation of the motor shaft to the webbing.6. The motorized seat belt retractor of claim 5, wherein said mechanismcomprises a gear train which couples the shaft of the motor to a spoolon which the webbing is wound.
 7. The motorized seat belt retractor ofclaim 6, wherein said mechanism includes a locking mechanism to preventthe motor shaft from rotating in a direction corresponding to thewebbing being withdrawn.
 8. The motorized seat belt retractor of claim1, wherein the load limiter is configured to increase the forcegenerated by the motor at a rate based on the weight of a vehicleoccupant.
 9. The motorized seat belt retractor of claim 8, furthercomprising an electrical controller.
 10. The retractor of claim 9,wherein the load limiter only utilizes the force generated by the motor.